Loop-around testing is frequently performed in switching networks to verify correct network operation. A test signal is generated at a test source, transmitted via the particular network path being tested to a destination, and then looped from the destination back to the test source. The source compares the returned signal with the transmitted test signal to verify the network path. Although loop-around techniques have been used most extensively in circuit switching networks implemented using either analog or digital switching elements, such techniques are also used to advantage to verify the communication of packets in, for example, the packet switching network of U.S. Pat. No. 4,486,877 issued to J. S. Turner on Dec. 4, 1984. Test packets are transmitted from a central processor associated with the Turner network to various network destinations, and then looped back to the central processor. Although loop-around tests efficiently detect the presence or absence of faults in a network, additional measures are typically required to determine the location of faults once they are detected.
Fault location information is important in packet networks not only to allow repair or replacement of defective equipment but also to allow rapid packet routing adjustments to be made within the network. Fault location measures are typically expensive and time-consuming, particularly in large regional or national packet networks, and in distributed packet networks where the switching nodes operate without a network central processor and individual nodes are in most cases unaware of the overall network topology.
In view of the foregoing, a recognized problem in the art is the need to conduct additional tests to isolate faults in a packet switching network once such faults have been detected.